PURPOSE: To detect the direction and speed of rotation of a rotator with one piece of detector by providing objects to be detected of different lengths to the rotator spacially at prescribed intervals, and detecting these with the detector.

CONSTITUTION: A rotator 11 is provided with objects 12 to be detected of different lengths spacially at prescribed intervals. A detector 13 is provided near said rotator 11. When the rotator 11 rotates, signals are outputted from the detector 13. The periods of the signals are inversely proportional to the rotating speed of the rotator 11, and are proportional to the size of the objects 12. The detected outputs are time-integrated by an integrator 14, and are removed of erroneous voltage by a voltage comparator 15. The output of the comparator 15 and the outputs of the detector 13 are discriminated by a pattern discriminator 16, and the rotating direction is detected by the discriminated output voltage. The rotating direction output from the discriminator 16 and the rotating speed output from the detector 13 are supplied to an output part 17, and the rotating speed corresponding to the rotating direction is outputted from the part 17.